Systems and methods for object localization and path identification based on RFID sensing

ABSTRACT

A networked radio frequency identification system includes a plurality of radio frequency identification (RFID) tag readers, a computer in signal communication with the RFID tag readers over a network, and a software module for storage on and operable by the computer that localizes RFID tags based on information received from the RFID tag readers using a network model having endpoints and oriented links. In an additional example, at least one of the RFID tag readers includes an adjustable configuration setting selected from RF signal strength, antenna gain, antenna polarization, and antenna orientation. In a further aspect, the system localizes RFID tags based on hierarchical threshold limit calculations. In an additional aspect, the system controls a locking device associated with an access point based on localization of an authorized RFID tag at the access point and reception of additional authorizing information from an input device.

FIELD OF THE INVENTION

This invention relates generally to object localization and path identification and, more specifically, to object localization and path identification based on radio frequency identification (RFID) sensing.

BACKGROUND OF THE INVENTION

Systems and methods for localizing objects using RFID sensing tend to be limited to simple location determination and do not typically allow for dynamic sensing reconfiguration based on varying application demands.

SUMMARY OF THE INVENTION

In one example, the present invention comprises a networked radio frequency identification system that includes a plurality of radio frequency identification (RFID) tag readers, a computer in signal communication with the RFID tag readers over a network, and a software module for storage on and operable by the computer that localizes RFID tags based on information received from the RFID tag readers using a network model having endpoints and oriented links.

In accordance with an additional example of the invention, the software module is configured to determine a semantic attribute of RFID tag movement. In one example, the semantic attribute is selected from movement into or out of a previously defined area.

In accordance with an additional example of the invention, the software module is configured to restrict or allow access to an access point to authorized RFID tags (access control). In one example, the software module accepts time intervals from a user along with access restriction/authorization rules associated with the time intervals as well as identification information related to the RFID tags or groups of RFID tags to be restricted/authorized. The software module restricts/authorizes access based on the time intervals, their associated access restriction/authorization rules, and the RFID tag information. Access points include, for example, access doors, barriers, and access gates. In addition, tracking points within an area may also be monitored.

In accordance with further examples of the invention, at least one of the RFID tag readers includes an adjustable configuration setting selected from RF signal strength, antenna gain, antenna polarization, and antenna orientation. In one example, the software module adjusts the adjustable configuration setting based on input from a user. However, the software module may also adjust the configuration setting based on other configuration settings or based on computed values during runtime. In an additional example, the software module is configured to accept time intervals from a user along with security levels that are associated with the time intervals and the software module adjusts the configuration setting based on the time intervals and their associated security levels.

In accordance with other examples of the invention, the system localizes RFID tags based on information received from the RFID tag readers using hierarchical threshold limit calculations. In one example, the hierarchical threshold limit calculations are based on accumulated reading factors from groups of settings for the RFID tag readers. In an additional example, the software module is configured to collect data for each setting of the RFID tag readers during an interval of time and calculate an aggregate result for each RFID tag reader based on an algorithm that uses a weighting function that includes W_(k,l) and NR_(k,l) as parameters where NR_(k,l) represents the number of RFID tag readings at an interrogator ‘k’ configured with a setting ‘l’ and W_(k,l) represents a weighting factor assigned to the interrogator ‘k’ configured with the setting ‘l’, and the algorithm spans all settings ‘l’ for the interrogator ‘k’. The software module in this additional example is further configured to aggregate the calculated aggregate results based on a second weighting function to determine an aggregation result for an endpoint and compare the aggregation result for the endpoint to at least one of a threshold value or threshold interval to determine whether the RFID tag is localized at the endpoint.

In accordance with further examples of the invention, the hierarchical threshold limit calculations are based on accumulated reading factors from settings of groups of RFID tag readers. In one example, the software module is configured to collect data for each group setting of a group of RFID tag readers during an interval of time and calculate an aggregate result for each group setting based on an algorithm that uses a weighting function that includes W_(k,l) and NR_(k,l) as parameters where NR_(k,l) represents the number of RFID tag readings at an interrogator ‘k’ configured with a group setting ‘l’ and W_(k,l) represents a weighting factor assigned to the interrogator ‘k’ configured with the group setting ‘l’, and the algorithm spans all group settings ‘l’ for the interrogator ‘k’. The software module in this example is further configured to aggregate the calculated aggregate results based on a second weighting function to determine an aggregation result for an endpoint and compare the aggregation result for the endpoint to at least one of a threshold value or threshold interval to determine whether the RFID tag is localized at the endpoint.

In accordance with yet other examples of the invention, the system localizes RFID tags based on information received from the RFID tag readers using probabilistic threshold calculations. In one example, the probabilistic threshold calculations are based on accumulated probabilities from groups of settings for RFID tag readers. In an additional example, the software module is configured to collect data for each setting of the RFID tag readers during an interval of time and calculate an aggregate result for each RFID tag reader based on an algorithm that uses a weighting function that includes W_(k,l) and P_(k,l) as parameters where P_(k,l)=PF_(k,l) (NR_(k,l), C_(k,l)) is the probability that the RFID tag is at endpoint E_(i) as detected from interrogator ‘k’ with settings ‘l’ calculated with the function PF_(k,l) with NR_(k,l) representing the number of RFID tag readings at interrogator ‘k’ configured with settings ‘l’ and C_(k,l) representing a reference reading value for interrogator ‘k’ configured with settings ‘l’ and where W_(k,l) represents a weighting factor assigned to the interrogator ‘k’ configured with the settings ‘l’, and the algorithm spans all settings ‘l’ for the interrogator ‘k’. The software module in this additional example is further configured to aggregate the calculated aggregate results based on a second weighting function to determine an aggregation result for an endpoint and compare the aggregation result for the endpoint to at least one of a threshold value or threshold interval to determine whether the RFID tag is localized at the endpoint.

In accordance with additional examples of the invention, the probabilistic threshold calculations are based on accumulated probabilities from settings of groups of RFID tag readers. In one example, the software module is configured to collect data for each group setting of a group of RFID tag readers during an interval of time and calculate an aggregate result for each group setting based on an algorithm that uses a weighting function that includes W_(k,l) and P_(k,l) as parameters where P_(k,l)=PF_(k,l)(NR_(k,l), C_(k,l)) is the probability that the RFID tag is at endpoint E_(i) as detected from interrogator ‘k’ with group settings ‘l’ calculated with the function PF_(k,l) with NR_(k,l) representing the number of RFID tag readings at interrogator ‘k’ configured with group settings ‘l’ and C_(k,l) representing a reference reading value for interrogator ‘k’ configured with group settings ‘l’ and where W_(k,l) represents a weighting factor assigned to the interrogator ‘k’ configured with the group settings ‘l’, and the algorithm spans all group settings ‘l’ for the interrogator ‘k’. The software module in this example is further configured to aggregate the calculated aggregate results based on a second weighting function to determine an aggregation result for an endpoint and compare the aggregation result for the endpoint to at least one of a threshold value or threshold interval to determine whether the RFID tag is localized at the endpoint.

In accordance with still further examples of the invention, the system includes a plurality of radio frequency identification (RFID) tag readers, a computer in signal communication with the plurality of RFID tag readers over a network, a locking device associated with an access point, the locking device in signal communication with the computer, an input device in signal communication with the computer, and a software module for storage on and operable by the computer. In some embodiments, multiple access points may be included and multiple locking devices and/or input devices may be associated with each access point. In one example, the software module localizes an authorized RFID tag at the access point based on information received from at least one of the plurality of RFID tag readers, receives additional authorizing information from the input device, and sends an unlock signal to the locking device based on the localization of the authorized RFID tag at the access point and the additional authorizing information.

In accordance with yet other examples of the invention, the input device includes a keypad and the additional authorizing information includes an access code. In some embodiments, the input device may include a keypad terminal, a computer, a touchscreen, or other components.

In accordance with still another example of the invention, the input device includes a mobile communications device, the software module is configured to send a request for an access code to the mobile communications device after the authorized RFID tag is localized at the access point, and the additional authorizing information includes the requested access code transmitted from the mobile communications device. In another example, the additional authorizing information may be received by the software module before the RFID tag is localized. The authorization message received from the mobile device may be valid for a predefined period of time, for example during which the RFID tag would need to be localized at the access point for an unlock signal to be sent to a locking device associated with the access point. In still another example, rather than an access code being received from the mobile device, an empty message might be received from a phone number associated with the mobile device, with the authorizing information being the phone number of the message itself.

In accordance with still another example of the invention, the input device includes a location enabled mobile communications device with global positioning system (GPS) capability, the software module is configured to receive or retrieve the location information from the mobile communications device after the authorized RFID tag is localized at the access point, and the additional authorizing information is computed based on the location information received from the mobile communications device.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred and alternative embodiments of the present invention are described in detail below with reference to the following drawings:

FIG. 1 is a diagram illustrating an environmental view of a system formed in accordance with an embodiment of the invention that is installed in a structure;

FIGS. 2A and 2B are diagrams showing additional detail for a portion of FIG. 1; and

FIGS. 3-6 are diagrams showing examples of network models in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a block diagram showing an environmental view of a system 20 formed in accordance with an embodiment of the invention that is installed in a structure 22. Although a transceiver is preferred, a separate transmitter and receiver may alternatively serve as a transceiver within the scope of this invention.

The system 20 includes a plurality of radio frequency (RF) readers, each of which is associated with at least one interrogator. Each interrogator includes a transceiver and an antenna. Each interrogator (including transceiver and antenna) or only the interrogator's antenna may be external to the associated RF reader or embedded within the RF reader. The system 20 as shown includes three RF readers 24 a, 24 b, and 24 c, each of which include two interrogators 26 that have antennas external to the RF readers 24 a, 24 b, and 24 c. Transceiver components (not shown) of the interrogators 26 are embedded within the RF readers 24 a, 24 b, and 24 c and are in signal communication with their associated antennas. Although the interrogators 26 are numbered the same, they might have differing technical characteristics in some embodiments. The system 20 also includes an RF reader 28 that has two embedded interrogators 30, five RF readers 32 a, 32 b, 32 c, 32 d, and 32 e that each has three embedded interrogators 30, and an RF reader 34 that has one embedded interrogator 30.

The system 20 also includes a computer 36 that has a processor 38 in data communication with a memory unit 40 and a storage device 42 also in data communication with the processor 38. In an example embodiment, the computer 36 is an application and database server. Additional computers or computer banks are also present in some embodiments. The computer 36 is in signal communication with a network 44. The network 44 is a wired network in an example embodiment, but is a wireless network in other embodiments. The RF readers 24 a, 28, and 32 a are also in signal communication with the network 44. The RF readers 24 b, 32 b, and 32 c are in signal communication with a concentrator 46 a. A concentrator is a computer that handles a set of RF readers and that may control parameters or settings of interrogators associated with any RF readers the concentrator handles. A concentrator may also issue commands to access doors and/or locking devices and receive feedback from them. The concentrator 46 a is also in signal communication with the network 44. The RF readers 24 c, 32 c, 32 d, 32 e, and 34 are in signal communication with a concentrator 46 b that is also in signal communication with the network 44.

In the example shown in FIG. 1, the RF readers 24 a and 28 are positioned outside an entrance to the structure 22. A door 50 located at the entrance leads to a first end of a first hallway within the structure 22. The RF readers 32 a and 32 b are positioned along the first hallway within the structure 22. The RF reader 24 b is shown outside the structure 22, but the antennas of the interrogators 26 associated with the RF reader 24 b are positioned along the first hallway within the structure 22. The RF reader 32 c is positioned toward a second end of the first hallway, but is also positioned at a first end of a second hallway within the structure 22 that is oriented at a right angle to the first hallway. The RF readers 32 d, 32 e, and 34 are positioned along the second hallway within the structure 22. A door 52 is located at a second end of the second hallway. The door 52 controls access to a room 54 located within the structure 22. The antennas of the interrogators 26 associated with the RF reader 24 c are positioned within the room 54. Although a specific configuration of RF readers, concentrators, and interrogators is shown, it should be understood that alternative configurations are used in other embodiments. Some embodiments do not use concentrators, for example. Other embodiments have the readers and/or the concentrators connected point to point in a mesh topology.

The system 20 also includes a locking device 60 that is associated with the door 50. The locking device 60 is in signal communication with the computer 36 over the network 44 (connection not shown) and is selectively locked and unlocked based on information received at the computer 36 from RF readers positioned near the door 50. Although the locking device 60 is controlled by the computer 36 in this embodiment, in other embodiments the locking device 60 is in signal communication with one or more RF readers or one or more concentrators that control the locking device 60 in a decentralized fashion. A locking device 63, similar to the locking device 60, is associated with the door 52 so that the system 20 is able to selectively control access to the room 54. A first input device 62, such as a keypad or touchscreen for example, is positioned outside the structure 22 near the door 50. The first input device 62 is in signal communication with the computer 36 over the network 44 (connection not shown). In some embodiments, the input device 62 is connected to a concentrator or to a computer (not shown) other than the computer 36. A second input device 64, such as a keypad or touchscreen for example, is positioned inside the structure 22 near the door 50. The second input device 64 is in signal communication with the computer 36 over the network 44 (connection not shown). In some embodiments, the input device 64 is connected to a concentrator or to a computer (not shown) other than the computer 36.

The system 20 is configured to work with one or more RFID tags 70 that typically include unique identifiers and may include other information. In an example embodiment, an RFID tag 70 is carried by a person that travels into, out of, and within the structure 22. However, in other embodiments, RFID tags are also associated with non-human objects. The RFID tags may also be embedded in cards, clothing, devices, vehicles, or other objects in some embodiments. In one embodiment, the RFID tag 70 is a passive RFID device. However, other embodiments may be configured to locate non-passive RFID devices. The system 20 is also configured to interact with a mobile communications device 72 in some embodiments. In one example, a software module localizes an authorized RFID tag at an access point such as the door 50 based on information received from at least one of the plurality of RFID tag readers, receives additional authorizing information from an input device, and sends an unlock signal to a locking device such as the locking device 60 based on the localization of the authorized RFID tag at the access point and the additional authorizing information. Since RFID tags recognized by the system typically include unique identifiers, different levels of access can be assigned to users or groups of users that have been assigned particular RFID tags. In one example, the additional authorizing information includes an access code received at an input device such as the first input device 62. In an additional example, the additional authorizing information includes an access code first transmitted to a mobile communications device such as the device 72 by the system 20 which is then entered at the first input device 62. In an additional example, an access code is entered into the device 72 and transmitted to the system 20.

One exemplary manner of operation is as follows. Once the RFID tag 70 is detected near the door 50, an appropriate signal is sent to the computer 36. In some embodiments, the tag 70 might also have associated access control rules at the door 50. Separately, the user associated with the tag 70 may send a signal via email or cell phone (for example) that is received at the computer 36 over a network such as an external phone or data network (not shown). The computer 36 searches one or more stored databases of RFID data and compares the stored data with the received secondary signals. For example, the RFID tag 70 may be paired with a cell call from a specific phone number, or receipt of an email from a particular email address with “unlock” or other known subject headers. If both the RFID tag 70 is sensed and the secondary access code or message is received, the door 50 is caused to be unlocked by the computer 36. If the RFID tag 70 is sensed but no code received, the computer 36 may automatically send an email, text message, or other signal to the user associated with the tag 70 to prompt the user to send the secondary access code.

A second exemplary manner of operation is as follows. Once the RFID tag 70 is detected near the door 50, an appropriate signal is sent to the computer 36. Separately, the user associated with the tag 70 may have a location enabled device that provides global location information such as GPS coordinates that is received at the computer 36 over a network such as an external phone or data network (not shown). The computer 36 compares the location information from the mobile device to the location of the detected RFID tag and if the locations are close to one another (within a predetermined range), the door 50 is unlocked by the computer 36. If the RFID tag 70 is sensed but no mobile device location is received or can be retrieved, or the locations don't match within the predetermined range, the computer 36 may automatically send an email, text message, or other alarm signal to the user associated with the tag 70 or to other personnel.

Typically, subjects that include employees, visitors, assets, cars, and other objects are assigned an RFID tag that is used to identify it to the system 20.

FIGS. 2A and 2B are diagrams showing additional detail for a portion of the system 20 and the structure 22 near the room 54 in an example embodiment. The RF readers 32 e and 34 are shown, as well as the antennas of the interrogators 26 associated with the RF reader 24 c. A subject with an RFID tag 70 is shown outside the room 54 near the door 52. As the tag 70 is detected by the RF readers 32 e and 34, the system 20 indicates that the subject is at a first endpoint, designated as E1. In FIG. 2A, the antenna of interrogator 30 associated with the reader 34 is oriented at approximately a 90 degree angle from the wall to which the reader 34 is attached. FIG. 2B is substantially similar to FIG. 2A, except that the antenna of the interrogator 30 associated with the reader 34 is oriented at approximately a 45 degree angle from the wall to which the reader 34 is attached such that the antenna points in the general direction of E1. Movement of the tag 70 into the room 54 causes the RF reader 24 c to detect the tag 70, at which time the system 20 indicates that the subject is at a second endpoint designated as E2A. The system also indicates that the tag just moved from E1 to E2A with an identifier designated as Link1. Additional movement of the tag 70 within the room 54 is also tracked by the RF reader 24 c such that the subject and tag 70 may be identified as being associated with an additional endpoint E2B or E2C (links to other endpoints not shown) as they move about the room 54.

Sensing at each endpoint is done using one or more RF interrogators. Each interrogator includes a transceiver and an antenna. The interrogator antennas emit electromagnetic waves generated by the transceiver which, when received by an RFID tag or card, eventually activates the tag or card. Once the tag is activated, it reflects a wave with encoded data that is received by the interrogator. Each interrogator has a number of settings, each with an associated weight. The settings include transmitted RF output power (RF signal strength), antenna gain, antenna polarization and antenna orientation. RF settings may change very rapidly in order to allow a broad range of collection data. The weights associated with the RF settings are used by a localization engine to compute a value using eligibility calculations that determines the location of an object in space if it is within a threshold interval associated with a specific location. The localization engine computes collected data received from the interrogators and aggregates the results. The aggregate result is then used to determine the location and movement of subjects.

In the example shown in FIGS. 2A and 2B, the RF reader 24 c localizes the tag 70 by transmitting and receiving RF signals using the interrogators 26. Each of the two antennas of the interrogators 26 associated with the RF reader 24 c is positioned with a different position and orientation. The received RF signal strength from the tag 70 varies at each of the two interrogators 26 depending on the location of the tag 70 within the room 54 and the current RF settings of each interrogator 26. The number of reads in a predetermined time period at each interrogator 26 also varies depending on similar factors. The localization engine then localizes the tag 70 within the room 54, such at a location associated with E2A, E2B, or E2C based on the received RF signal strength and/or number of reads received at each interrogator 26 for particular RF settings.

FIGS. 3-6 are diagrams illustrating examples of network models in accordance with an embodiment of the invention. Each network model includes one or more endpoints. Each endpoint has an associated physical location or area in space and is represented in the network model as a graph node. Two endpoints and their sequence define an oriented link that is mapped to an oriented link in the graph. The network model may be hierarchical, on multiple levels, in the sense that at a higher level one graph node (endpoint) may represent a collection of nodes (endpoints) of a lower level with better resolution. An installed system is represented as a facility space network model that includes a series of endpoints (nodes) and their connected oriented links. As such, at each level, the facility space network model resembles a spatial graph.

With respect to FIG. 3, the diagram includes first, second, third, and fourth endpoints designated as EP1, EP2, EP3, and EP4 respectively. Each of the four endpoints is associated with a corresponding physical location that is labeled as location 1 through location 4 respectively. Oriented links labeled Link1 through Link6 are shown that represent possible paths that an RFID tag could take between spatial locations associated with the endpoints. EP1, EP2, and EP3 are shown within a box labeled Access Area A. In one example, location 4 is inside a room 80 having an entrance with a door 82 (shown partially open) and Access Area A corresponds to an area outside of the room 80 near the door 82. In an example embodiment, a system, such as the system 20 described with respect to FIG. 1 is used to localize an RFID tag within and outside the room 80 at locations one through four and other locations, using RF readers (not shown) in a similar manner to that described with respect to FIGS. 1, 2A, and 2B.

FIG. 4 is an example of a higher level network model used in conjunction with the model represented in FIG. 3 to form a hierarchical network model. FIG. 4 includes a fifth node and a sixth node designated as EP5 and EP6, respectively. EP5 represents all of the nodes EP1, EP2, and EP3, and EP6 represents EP4 and any location inside the room 80 shown in FIG. 3. Oriented links, labeled Link7 and Link8 are shown that represent possible paths that an RFID tag could take between spatial locations associated with EP5 and EP6.

With respect to FIG. 5, the diagram includes first, second, third, and fourth endpoints designated as EP7, EP8, EP9, and EP10 respectively. Each of the four endpoints is associated with a corresponding physical location that is labeled as location 7 through location 10 respectively. Oriented links are shown that represent possible paths that an RFID tag could take between spatial locations associated with the endpoints. EP7 is shown within a box labeled Access Area B. In one example, locations 8, 9 and 10 are inside a room 90 having an entrance with doors 92 and 93 (shown partially open) and Access Area B corresponds to an area outside of the room 90 near the doors 92 and 93. In an example embodiment, a system, such as the system 20 described with respect to FIG. 1 is used to localize an RFID tag within and outside the room 90 at locations seven through ten and other locations, using RF readers (not shown) in a similar manner to that described with respect to FIGS. 1, 2A, and 2B.

FIG. 6 is an example of a higher level network model used in conjunction with the model represented in FIG. 5 to form a hierarchical network model. FIG. 6 includes a node designated as EP11 and a node designated as EP12. EP11 represents EP7 and any location inside Access Area B shown in FIG. 5. EP12 represents all of the nodes EP8, EP9, and EP10, and any location inside the room 90. Oriented links, labeled Link15 and Link16 are shown that represent possible paths that an RFID tag could take between spatial locations associated with EP11 and EP12. A hierarchical model such as that represented by FIGS. 5 and 6 allows different semantics of movement to be associated with each level. For example, Link9 and Link11 shown in FIG. 5 might represent semantic attributes of ‘IN DOOR 92’ and ‘IN DOOR 93’, respectively while Link15 shown in FIG. 6 might represent ‘ENTER ROOM 80’. Although FIG. 6 is one example of a higher level network model corresponding to the model shown in FIG. 5, other models could be used in other embodiments. Additionally, more than two levels may be used in some hierarchical network models.

In an example embodiment, the network model is organized as a graph and a semantic engine computes semantic rules based on attributes of elements in the network model graph. In some embodiments, the network model has a hierarchical structure on multiple levels. Semantic rules are both statically defined and learned by the semantic engine while the system is running in an example embodiment. An example of a statically defined semantic rule is that if a subject with an RFID tag passes an oriented link in the model and that link has an ‘IN’ attribute associated with it, the semantic engine will interpret that movement as an entrance event into the space represented by the destination node, or, more generally, into a larger space in which the space represented by the destination node is located if the ‘IN’ attribute includes additional information such as an ‘IN’ attribute labeled ‘INTO ROOM’ or ‘INTO BUILDING’, for example. For example, movement from EP2 to EP4 might represent an entrance event into the room 80, with Link5 having an attribute labeled ‘INTO ROOM’ associated with it. In this example, the semantic engine would interpret movement of a subject with an RFID tag from EP2 to EP4 as an entrance event into the room 80. This semantic attribute is an indicator of movement from outside the room 80 to inside the room 80, rather than simply an indicator that the detected tag is in the room 80.

Movement into and out of spaces larger than those represented by destination nodes may be identified in other manners in some embodiments. For example, an entrance event into the room 80 may be identified based on Link5 having an attribute labeled ‘IN’ if location 4 is mapped to the room 80 and the semantic engine uses this mapping along with the ‘IN’ attribute of Link5 to identify the entrance event. In some embodiments, direction of movement can also be considered to be a semantic event, such as ‘walk front to back in a particular area’ or ‘walk north’, for example. In embodiments where a hierarchical network model is used, the semantic engine may use the semantics of any level or combination of levels to identify any semantic events. For example, the semantic of movement from EP2 to EP4 at the level shown in FIG. 3 is of movement from location 2 to location 4. However, at a higher level (as represented in FIG. 4) the movement from EP2 to EP4 maps as a movement from EP5 to EP6 and the semantic might be of entrance into the room 80. Further still, at an even higher level (not represented here) the semantic might be of entrance into a building where the room 80 is located. The semantic engine infers the semantics of an action using the hierarchical model.

Learned semantic rules are determined by the system at runtime using inputs and observations. An example of a learned semantic rule is when a subject with an RFID tag is preparing to leave a building through an access door, but is required by the system to enter the semantics passing through the door before being allowed to pass through the door and consequently a link in the network graph. The subject may specify that it is a break event by using a keypad, touchscreen, or other input device such as the keypad 64 shown in FIG. 2 before passing through the door 50. The semantic engine then determines that passing that link in the network graph represents an exit event (OUT event). In one example, time values are also recorded by the system 20 for some or all localization determinations and semantic attribute determinations. These time values may be stored in association with an identifier associated with an RFID tag that had been localized or that had received a semantic attribute determination. The time values may be set to expire after a certain period of time, may only apply to particular semantic attributes or particular RFID tags, may be stored in a system database and/or log and/or be used to calculate (time) tracking data.

A software module (having an access control engine component) restricts or allows access at an access point based on access control rules associated with elements in the network model graph. Access control rules are based on configuration settings and/or they may be defined by a user and saved in the configuration settings. Access control rules are associated with oriented links in the network model. An example of a defined access control rule is that an RFID tag is allowed to pass an oriented link only if it is authorized to do so. In another example, an RFID tag may be authorized to pass an oriented link in the network model only in certain periods of time during a day if the user has defined time restriction intervals on the access path represented by the oriented link. The access control rules might be specific for each RFID tag or group of RFID tags or may be general. The access control rules might also be associated with additional authorization information such as entering an additional access code, mobile device authentication information, or global positioning location matching, for example. In one example, time values are also recorded by the system 20 for some or all access events (lock/unlock/door open) and access control determinations. These time values may be stored in association with an identifier associated with an RFID tag that had been allowed or restricted access. The time values may be set to expire after a certain period of time, may only apply to particular access events or particular RFID tags, may be stored in a system database and/or log and/or used to calculate tracking data.

In one example, the system 20 is configured to localize an RFID tag at an endpoint by using hierarchical threshold limit calculations based on accumulated reading factors from groups of settings for RF interrogators. In one instance, localization of an RFID tag at E2A, E2B, or E2C as shown in FIGS. 2A and 2B could be performed by the RF reader 24 c in this manner. In an alternate example, the system 20 is configured to use hierarchical probabilistic threshold calculations based on accumulated probabilities from groups of settings for RF interrogators. In an additional example, the system 20 is configured to use hierarchical threshold limit calculations based on accumulated reading factors from settings of groups of RF interrogators. In a further example, the system 20 is configured to use hierarchical probabilistic threshold calculations based on accumulated probabilities from settings of groups of RF interrogators. Each of the four examples is discussed in greater detail below. In each of the four examples, there are ‘n’ RF interrogators in the system designated as RF₁, RF₂ . . . RF_(n). There are ‘m’ endpoints defined in a network model, designated as E₁, E₂ . . . E_(m). There is one RFID tag in range of the system, and the system validates the tag's location as being at endpoint E_(i). Although only one RFID tag is discussed for simplicity, it should be understood that multiple RFID tags can be tracked by the system 20.

In the first example, the system uses hierarchical threshold limit calculations based on accumulated reading factors from groups of settings for RF interrogators. In this approach each interrogator has an assigned collection of settings/configurations. For example, RF_(i) might have an assigned collection including two settings while RF_(j) might have a collection including five settings, with a setting being defined by values of any of the RF interrogator parameters or a combination of parameters such as transmitted RF power output, antenna gain, antenna polarization, and antenna orientation. There is also a weight associated with each setting of the RF interrogator, designated as W_(k,l) where ‘k’ is the index for the RF interrogator and ‘l’ is the index for the interrogator's setting. For an endpoint E_(i), there is a threshold value or interval (Tv) used in assessing whether a subject with an RFID tag is located at the endpoint. A threshold value or interval is also used in the other examples, but the particular value or interval may vary in each example.

In an interval of time, the system collects data for each setting of the RF interrogators with NR_(k,l) representing the number of tag readings at the interrogator ‘k’ configured with the settings ‘l’ during the time interval. In a first step for endpoint E_(i), the system calculates an aggregate result for each interrogator based on a weighting formula/function: A_(k)=F_(k)(W_(k,l), NR_(k,l)) where ‘k’ is the interrogator index and ‘l’ spans all settings for interrogator ‘k’. A second step includes aggregating the results obtained in the first step based on a weighting fonnula/function: A=G (WA_(k), A_(k)) where ‘k’ is the interrogator index and WA_(k) is the weight associated with the interrogator k at the endpoint E_(i). The aggregation result A is then compared with the threshold value or interval Tv to assess whether the tag is localized at endpoint E_(i).

One example implementation of this first example can be described with reference to FIGS. 2A and 2B. The endpoint of interest Ei is E1. A RFID tag located at E1 may be read by all the interrogators 30 and 26. The interrogator 30 in reader 34 is assigned four settings: one setting for which the antenna is oriented as in the FIG. 2A with RF power output 36 dBm, one setting for which the antenna is oriented as in the FIG. 2A with RF power output 33 dBm, one setting for which the antenna is oriented at a 45 degree angle towards E1 as in FIG. 2B with RF power output 36 dBm and one setting for which the antenna is oriented at a 45 degree angle towards E1 as in FIG. 2B with RF power output 33 dBm. The antenna of the interrogator 30 associated with the reader 34 has vertical polarization. All the other interrogators have just one setting, with the antennas' orientations as shown in FIG. 2A and an RF power output of 33 dBm. All the interrogators' antennas have a fixed gain of 6 dBi. The interrogators 30 in the reader 32 e have different antenna polarizations, one vertical, one horizontal and one circular. The first two settings of the interrogator 30 associated with the reader 34, corresponding to the antenna orientation shown in FIG. 2A, are assigned negative weights W1,1=(−0.4) and W1,2=(−0.5) because the antenna is vertically polarized and does not point toward E1, in such a way that it detects tags located away from E1. For the next two settings, the weights are higher and set at W1,3=0.5 and W1,4=0.4 respectively, because the antenna points toward EP1 and detects tags around EP1.

While the antennas may be oriented in a physical manner that directs them in an angular fashion such that the point toward a desired direction, it should be understood that they may alternatively (or in addition) be electronically steerable to encompass a preferred field of view.

The first two settings of the interrogator 30 associated with the reader 34 are used to detect that the tag is not likely at endpoint E1 but rather in the coverage area for this setting away from E1, because the interrogator antenna is oriented away from the location of E1; hence these settings have associated negative weights. For all the interrogators in reader 32 e, there is a single setting with a weight of 0.8 (W2,1, W3,1, W4,1 are all 0.8). For E1, all the interrogators in reader 24 c have null weights(0). The weights are calculated and determined using site surveys and simulations, for example. Weights associated with other functions and examples are determined in a similar fashion.

During an interval of time, such as 1 ms for example, the system collects data from all settings from all readers. For the interrogator 30 associated with the reader 34, it collects reading values for each setting and aggregates the values using an aggregation function. The aggregation function(F) for each interrogator for this example may be viewed as a sum of weights applied to the number of tag reads. In other examples, the aggregation functions for each interrogator might be different from each other. For the interrogator 30 associated with the reader 34, the readings are N1,1=16, N1,2=10, N1,3=2 and N1,4=0. For the interrogator 30 associated with the reader 34, the aggregate value becomes A1=W1,1*N1,1+W1,2*N1,2+W1,3*N1,3+W1,4*N1,4=(−0.4)*16+(−0.5)*10+0.5*2+0.4*0˜(−10.4). For the three interrogators 30 associated with the reader 32 e, the system collects one reading value N2,1=4, N3,1=2 and N4,1=0, respectively, with the not null readings coming from horizontally and circularly polarized antennas. The aggregate values for the interrogators 30 associated with the reader 32 e become A2=W2,1*N2,1=0.8*4=3.2, A3=W3,1*N3,1=0.8*2=1.6 and A4=W4,1*N4,1=0.8*0=0, respectively. For the interrogators 26 associated with the reader 24 c, the collected data doesn't matter in this example calculation because the weights associated with the interrogators 26 are null (in this example those interrogators are not taken into consideration while calculating position at E1). The final result is then computed as an aggregation of the particular results normalized with the weight associated with each interrogator.

The final aggregation function(G) for this example is a sum of the weights applied to the aggregated values for each interrogator from the previous step. In this example, the interrogator 30 associated with the reader 34 is assigned a weight of WA1=0.5, the interrogators 30 associated with the reader 32 e each have a weight of 0.6 (WA2, WA3, WA4 are all 0.6), and as mentioned above all the other interrogators have null weights. Using these weights, the final aggregate value become A=WA1*A1+WA2*A2+WA3*A3+WA4*A4=0.5*(−10.4)+0.6*3.2+0.6*1.6+0.6*0˜(−2.32). This value is compared with a previously determined threshold value Tv=1 which is assigned to E1. In this example, the threshold value is not reached which means that the subject is not in endpoint E1.

In the second example, the system uses hierarchical probabilistic threshold calculations based on accumulated probabilities from groups of settings for RF interrogators. This calculation is very similar with the previous one, except that in the first step of the calculations, weights are applied to a probability. For each interrogator setting there is a reference reading value that expresses the highest probability that the tag may be at endpoint E_(i). This is represented as C_(k,l) where ‘k’ is the index for the RF interrogator and ‘l’ is the index for the interrogator's setting. In a first step for endpoint E_(i), the system calculates an aggregate result for each interrogator based on a weighting formula/function: A_(k)=F_(k)(W_(k,l), P_(k,l)) where ‘k’ is the interrogator index, ‘l’ spans all settings for interrogator ‘k’ and P_(k,l)=PF_(k,l)(NR_(k,l),C_(k,l)) is the probability that the tag is at endpoint E_(i) as detected from interrogator ‘k’ in configuration ‘l’ calculated with the function PF_(k,l). A second step includes aggregating the results obtained in the first step based on a weighting formula/function: A=G(WA_(k), A_(k)) where ‘k’ is the interrogator index and WA_(k) is a weight associated with the interrogator ‘k’ at the endpoint E_(i). The aggregation result A is then compared with a threshold value or interval Tv to assess whether the tag is localized at endpoint E_(i).

An example implementation of this second example can be described with reference to FIGS. 2A and 2B. The endpoint of interest Ei is E1. A RFID tag located at EP1 may be read by all the interrogators 30 and 26. In this example, the interrogator 30 associated with the reader 34 is assigned four settings: one setting for which the antenna is oriented as shown in FIG. 2A with an RF power output of 36 dBm, one setting for which the antenna is oriented as shown in FIG. 2A with RF power output 33 dBm, one setting for which the antenna is oriented at a 45 degree angle towards E1 as shown in FIG. 2B with RF power output 36 dBm, and one setting for which the antenna is oriented at a 45 degree angle towards E1 as shown in FIG. 2B, with RF power output 33 dBm. For all settings, the antenna of the interrogator 30 associated with the reader 34 has vertical polarization. All of the other interrogators have just one setting, with the antenna orientation as shown in FIG. 2A, and an RF power output of 33 dBm. All of the interrogators' antennas have a fixed gain of 6 dBi. The interrogators 30 associated with the reader 32 e have different antenna polarizations, one vertical, one horizontal and one circular.

The first two settings of the antenna of the interrogator 30 associated with the reader 34 correspond to the antenna orientation as shown in FIG. 2A, and are assigned weights of W1,1=0.5 and W1,2=0.5. The reference reading values are low values of C1,1=1 and C1,2=0 because the antenna is vertically polarized and does not point toward EP1, such that it detects tags located away from E1. For the next two settings, the weights are higher W1,3=1 and W1,4=0.9 respectively and the reference reading values are higher values of C1,3=10 and C1,4=9, because the antenna points toward E1 and detects tags located near E1. For all of the interrogators 30 associated with the reader 32 e, there is a single setting with a weight of 0.9 (W2,1, W3,1, W4,1 are all 0.9) with a reference reading value of 12 (C2,1, C3,1, C4,1 are all 12). For E1, all of the interrogators 26 associated with the reader 24 c have null weights(0). The weights and the reference reading values are calculated and determined using site surveys and simulations, for example.

During an interval of time, such as 1 ms for example, the system collects data from all interrogators for all settings. For the interrogator 30 associated with the reader 34, the system collects reading values for each setting and aggregates the values using an aggregation function. The aggregation function(F) for each interrogator for this example is the average of the weights applied to the probability that the tag is at the endpoint E1 for each interrogator setting. The probability that the RFID tag is at endpoint E1 for each interrogator setting is computed based on a probability function P(N, C) which in this example is: for the first two settings of the interrogator 30 associated with the reader 34 (P1,1, P1,2)={0 if N>C, 0.5 if N<=C}; for the last two settings of the interrogator 30 associated with the reader 34 (P1,3, P1,4)={0 if N=0, C/N if N>C, N/C if N<=C }; and for all settings of the interrogators 30 associated with the reader 32 e (P2,1, P3,1, P4,1)={0 if N=0, C/N if N>C, N/C if N<=C}. For the interrogator 30 associated with the reader 34, the readings are N1,1=0, N1,2=0, N1,3=8 and N1,4=7. For the interrogator 30 associated with the reader 34, the aggregate value becomes A1=(W1,1*P1,1+W1,2*P1,2+W1,3*P1,3+W1,4*P1,4)/4=(0.5*0.5+0.5*0.5+1*8/10+0.9*7/9)/4=2/4=0.5. For the three interrogators 30 associated with the reader 32 e the system collects three reading values N2,1=14, N3,1=12 and N4,1=6, respectively. The aggregate values for the interrogators 30 associated with the reader 32 e become A2=(W2,1*P2,1)/1=0.9*12/14=0.77, A3=(W3,1*P3,1)/1=0.9*12/12=0.9 and A4=(W4,1*P4,1)/1=0.9*6/12=0.45 respectively. For the interrogators 26 associated with the reader 24 c, the collected data doesn't matter in this example calculation because the weights associated with the interrogators 26 are null (in this example those interrogators are not taken into consideration while calculating position at E1).

The final result is then computed as an aggregation of the particular results normalized with the weight associated with each interrogator. In this example, the interrogator 30 associated with the reader 34 has a weight of WA1=0.8, the interrogators 30 associated with the reader 32 e each have a weight of 0.9 (WA2, WA3, WA4 are all 0.9) and, as mentioned above, all the other interrogators have null weights. The final aggregation function (G) for this example is the average of the weights applied to the aggregated values for each interrogator from the previous step. The final aggregate value become A=(WA1*A1+WA2*A2+WA3*A3+WA4*A4)/4=(0.8*0.5+0.9*0.77+0.9*0.9 +0.9*0.45)/4=(0.40+0.69+0.81+0.41) /4˜0.57. This value is compared with a previously determined threshold value Tv=0.50 which is assigned to E1. In this example, the threshold value is reached which means that the subject is at endpoint E1.

In the third example, the system uses hierarchical threshold limit calculations base on accumulated reading factors from settings of groups of RF interrogators. In this approach a group of interrogators has an assigned collection with any number of settings/configurations. For example, four RF interrogators at an access door might have an assigned collection including two settings, with a setting being defined by the combination of any RF interrogators' parameters such as transmitted RF power output, antenna gain, antenna polarization, and antenna orientation. There is a weight associated with the endpoint E_(i) for each setting of a group of RF interrogators. There is also a weight associated with each interrogator from the group configured with each of the group settings; this is represented as W_(k,l) where ‘k’ is the index for an RF interrogator in the group and ‘l’ is the index for the group's setting. In an interval of time, the system collects data for each setting of the group of RF interrogators with NR_(k,l) representing the number of readings at the interrogator ‘k’ configured with the group setting ‘l’. In a first step for endpoint E_(i), the system calculates an aggregate result for each group setting based on a weighting formula/function: A_(l)=F_(k)(W_(k,l), NR_(k,l)) where ‘k’ is the interrogator index in the group and ‘l’ spans all settings for the interrogator group. A second step includes aggregating the results obtained in the first step based on a weighting formula/function: A=G(WA₁, A₁) where ‘l’ is the group setting index and WA₁ is a weight associated with the group setting ‘l’ at the endpoint E_(i). The aggregation result A is then compared with a threshold value/interval Tv to assess whether the tag is localized at endpoint E_(i).

An example implementation of this third example can be described with reference to FIGS. 2A and 2B. The endpoint of interest Ei is E1. A RFID tag located at E1 may be read by all the interrogators 30 and 26. All of the interrogators 30 represent a group used to detect whether the subject is at endpoint E1. The group of interrogators includes group settings, which are a collection of particular settings for each interrogator. In this example, two group settings are defined.

The first group setting includes: a setting for the interrogator 30 associated with the reader 34 where the antenna is oriented at a 45 degree angle towards E1 as shown in FIG. 2B, with interrogator RF power output 33 dBm and antenna polarization circular; a setting for each interrogator 30 associated with the reader 32 e where the antenna is oriented as in FIG. 2A, with interrogator RF power output 36 dBm and antenna polarization vertical. For this first group setting, the weight associated with the interrogator 30 associated with the reader 34 is W1,1=0.9 and the weights associated with the interrogators 30 associated with the reader 32 e (W1,2, W1,3, W1,4) are all 1, which means that all reads from all the interrogators in the group will count during the aggregation calculation for this group setting.

The second group setting includes: a setting for the interrogator 30 associated with the reader 34 where the antenna is oriented as in FIG. 2A, with interrogator RF power output 36 dBm and antenna polarization vertical; the settings for the interrogators 30 associated with the reader 32 e don't matter because these interrogators are associated weights of 0 for this group setting and they don't count during the aggregation calculation of this group setting. In this example, the second group setting may help detect that the tag is not likely to be at endpoint E1, but rather in the coverage area for this group setting away from E1 because the only interrogator antenna that counts is oriented away from the location of E1. However, this is just a particular case and should not limit the generality of the algorithm. For the second group setting, the weight associated with the interrogator 30 associated with the reader 34 is a negative value W2,1=−0.9 because the interrogator settings allow detection in an area away from EP1 and the weights associated with the interrogators 30 associated with the reader 32 e (W2,2, W2,3, W2,4) are all 0 which means that all the reads from the interrogators 30 associated with the reader 32 e will not count during the aggregation calculation for this group setting. In this example, all the interrogators' antennas have a fixed gain of 6 dBi.

In an interval of time, such as 1 ms for example, the system collects data from both group settings: for the first group setting the number of reads at the interrogator 30 associated with the reader 34 is N1,1=2 and for each interrogator 30 associated with the reader 32 e, the number of reads are N1,2=0, N1,3=1, N1,4=2, respectively. For the second group setting, the number of reads at the interrogator 30 associated with the reader 34 is N2,1=10 and for each interrogator 30 associated with the reader 32 e, the number of reads are N2,2=0, N2,3=1, N2,4=2, respectively. For each group setting, the system aggregates the values using an aggregation function. In this example, the aggregation functions(F) for each group setting can be considered as a sum of weights applied to the number of tag reads for each interrogator in the group. In other examples, the aggregation functions for each group setting might be different from each other.

For the first group setting, the aggregate value becomes A1=W1,1*N1,1+W1,2*N1,2+W1,3*N1,3+W1,4*N1,4=0.9*2+1*0+1*1+1*2=(4.8). For the second group setting, the aggregate value becomes A2=W2,1*N2,1+W2,2*N2,2+W2,3*N2,3+W2,4*N2,4=(−0.9)*10+0*2+0*1+0*0=(−9). The final aggregation function(G) for this example is the sum of the group settings' weights applied to the aggregated values for each group setting from the previous step. The first group setting is assigned a weight of WA1=0.9 while the second group setting is assigned a weight value of WA2=0.8. Any weight might have a positive or negative value. The final aggregate value become A=WA1*A1+WA2*A2=0.9*4.8+0.8*(−9)=(−2.88). This value is compared with a previously defined threshold value Tv=3 which is assigned to E1. In this example, the threshold value is not reached which means that the subject is not at endpoint E1.

In the fourth example, the system uses hierarchical probabilistic threshold calculations based on accumulated probabilities from settings of groups of RF interrogators. This calculation is very similar to the third example, except that in the first step of the calculations weights are applied to a probability. For each group setting there is an reference reading value that expresses the highest probability that the tag may be at endpoint E_(i), noted with C_(k,l) where ‘k’ is the index for an RF interrogator in the group and ‘l’ is the index for the group's setting. In a first step, the system calculates for endpoint Es an aggregate result for each group setting based on a weighting formula/function: A₁=F_(k)(W_(k,l), P_(k,l)) where ‘k’ is the interrogator index in the group, ‘l’ spans all settings for the interrogator group and P_(k,l)=PF_(k,l)(NR_(k,l), C_(k,l)) is the probability that the tag is at endpoint E_(i) as detected from interrogator ‘k’ in group configuration ‘l’ calculated with the function PF_(k,l). A second step includes aggregating the results obtained in the first step based on a weighting formula/function: A=G(WA₁, A₁) where ‘l’ is the group setting index and WA₁ is a weight associated with the group setting ‘l’ at the endpoint E_(i). The aggregation result A is then compared with a threshold value/interval Tv to assess whether the tag is localized at endpoint E_(i). In all of the configurations described with respect to the four examples, the weights and the threshold values including reference reading values can be statically defined and/or computed during execution using a learning algorithm.

An example implementation of this fourth example can be described with reference to FIGS. 2A and 2B. The endpoint of interest Ei is E1. A RFID tag located at E1 may be read by all the interrogators 30 and 26. All of the interrogators 30 represent a group used to detect whether the subject is at endpoint E1. The group of interrogators includes group settings which are a collection of particular settings for each interrogator. In this example, two group settings are defined.

The first group setting includes: a setting for interrogator 30 associated with the reader 34 where the antenna is oriented at a 45 degree angle towards E1 as shown in FIG. 2B, with interrogator RF power output 33 dBm and antenna polarization circular; a setting for each interrogator 30 associated with the reader 32 e where the antenna is oriented as shown in FIG. 2A, with interrogators RF power output 36 dBm and antenna polarization vertical. For this first group setting, the weight associated with the interrogator 30 associated with the reader 34 is W1,1=0.9 and the weights associated with interrogators 30 associated with the reader 32 e (W1,2, W1,3, W1,4) are all 1 which means that all the reads from all the interrogators will count during the aggregation calculation for this group setting. The reference reading value for the interrogator 30 associated with the reader 34 configured with this group setting is C1,1=10. This is a high value because the antenna in this setting is circularly polarized and points directly toward E1 such that it detects tags located near E1. For the other three interrogators in the group configured with this group setting, the reference values are C1,2=10, C1,3=10 and C1,4=9. These are high values because these interrogators' antennas point toward E1 and detect tags located near E1.

The second group setting includes: a setting for the interrogator 30 associated with the reader 34 where the antenna is oriented as shown in FIG. 2A, with interrogator RF power output 36 dBm and antenna polarization vertical. The settings for the interrogators 30 associated with the reader 32 e don't matter because these interrogators are associated with weights of 0 for this group setting and they don't count during the aggregation calculation of this group setting. For the second group setting, the weight associated with the interrogator 30 associated with the reader 34 is a lower value W2,1=0.4 because the interrogator settings allow detection in an area away from the E1 location and the weights associated with the interrogators 30 associated with the reader 32 e (W2,2, W2,3, W2,4) are all 0.9 which means that all the reads from the interrogators 30 associated with the readers 32 e will count during the aggregation calculation for this group setting. The reference reading value for the interrogator 30 associated with the reader 34 configured with this group setting is C2,1=0. This is a low value because the antenna in this setting is vertically polarized and points in a direction away from E1, such that it detects tags located away from E1. For the other three interrogators in the group configured with this group setting, the reference values are C2,2=10, C2,3=10 and C2,4=9. These are higher values because these interrogators' antennas point toward E1 such that they detect tags around EP1. In this example, all the interrogators' antennas have a fixed gain of 6 dBi.

In an interval of time, such as 1 ms for example, the system collects data from both group settings: for the first group setting the number of reads at the interrogator 30 associated with the reader 34 is N1,1=2 and for each interrogator 30 associated with the reader 32 e, the number of reads are N1,2=0, N1,3=1, N1,4=2 respectively. For the second group setting, the number of reads at the interrogator 30 associated with the reader 34 is N2,1=10 and for each interrogator 30 associated with the reader 32 e, the number of reads are N2,2=0, N2,3=1, N2,4=2 respectively.

For each group setting, the system aggregates the values using an aggregation function. The aggregation function(F) for each group setting for this example is the average of the weights applied to the probability that the tag is at the endpoint E1 for each interrogator setting. The probability that the RFID tag is at endpoint E1 for each interrogator configured with the group setting is computed based on a probability function P(N, C) which in this example is: for the first group setting of the interrogator 30 associated with the reader 34 (P1,1)={0 if N=0, C/N if N>C, N/C if N<=C}; for the second group setting of the interrogator 30 associated with the reader 34 (P2,1)={0 if N>C, 0.5 if N<=C}; and for all the interrogators 30 associated with the reader 32 e group settings (P1,2, P1,3, P1,4, P2,2, P2,3, P2,4)={0 if N=0, C/N if N>C, N/C if N<=C}.

For the first group setting, the aggregate value becomes A1=(W1,1*P1,1+W1,2*P1,2+W1,3*P1,3+W1,4*P1,4)/4=(0.9*2/10+1*0/10+1*1/10+1*2/9)/4˜0.52/4=0.13. For the second group setting, the aggregate value becomes A2=(W2,1*P2,1+W2,2*P2,2+W2,3*P2,3+W2,4*P2,4)/4=(0.4*0+0.9*0/10+0.9*1/10+0.9*2/9)/4˜0.29/4˜0.07. The final aggregation function (G) for this example is the average of the group settings' weights applied to the aggregated values for each group setting from the previous step. The first group setting is assigned a weight of WA1=0.9 while the second group setting is assigned a weight value of WA2=0.8. Any weight might have a positive or negative value in other examples.

The final aggregate value becomes A=(WA1*A1+WA2*A2)/0.2=(0.9*0.13+0.8*0.07)/2˜0.087. This value is compared with a previously defined threshold value Tv=0.50 which is assigned to E1. In this example, the threshold value is not reached which means that the subject is not at endpoint E1.

For each of the weighting formulas above, the weights are numerical values (real numbers). Any of the weights might have a positive or a negative value. An example of an aggregation function F or G) is a sum of weights applied to each number to be aggregated Funct(Wn, Nn)=SUM(Wn*Nn) where n is an integer. Another example of an aggregation function(G) is an average of weights applied to each number to be aggregated Funct(Wn, Nn)=SUM(Wn*Nn)/M where n is an integer spanning from 1 to M. Although specific values have been used in the examples above, it should be understood that the system is not limited to using the example values.

In an example embodiment, the system 20 is dynamically configurable to allow a system administrator, for example, to define intervals of time in which RFID tag reading at one or more endpoints is performed in a manner that is different then the manner in which RFID tags are read at the identified endpoints during other time intervals. This functionality can be used to provide more stringent security settings at differing times of day. The system adjusts the RF settings of the endpoint's RF interrogators and their associated weights to values that correspond to a desired level of RFID tag reading performance. As an example, for an endpoint used to read RFID tags for access to a building or room during off hours, the system settings may have high weights for settings corresponding to low transmitted RF output power, low antenna gain, and linear polarization of external interrogators at building access locations, but very low or null weights for other settings. This results in RFID tags being sensed at a shorter range during the off-hours interval than during the regular hours interval and requires a close proximity of an RFID tag to an external antenna before access is allowed. In one example, an RF signal strength setting is adjusted based on the received time interval and associated security level setting. In some embodiments, the time interval and associated security level setting may be entered once and kept in a system configuration. In other embodiments, the time interval and associated security level setting may be changed by the system administrator or other authorized users.

In one example, a system administrator defines a first regular-hours interval of time from 8 am-8 pm, a second off-hours interval from 8 pm-10 pm and a last interval from 10 pm to 8 am when no access is allowed. The system settings for the off-hours interval have high weights for settings corresponding to low transmitted RF output power, low antenna gain, and linear polarization of external interrogators at building access locations but very low weights or null weights for other settings. This results in RFID tags being sensed at a shorter range during the off-hours interval than during the regular-hours interval and requires a close proximity of an RFID tag to an external antenna before access is allowed. Alternatively, the system settings may be set such that RFID tags are more easily sensed at a longer range during the off-hours interval than during the regular-hours interval. This could possibly be desirable if an entrance were located such that many people with RFID tags pass by the entrance during the regular-hours interval without having an intention of entering, but people with RFID tags after-hours generally pass through the entrance if they are detected nearby.

While the preferred embodiment of the invention has been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. For example, functions performed by the computer 36 may be performed in a distributed manner in other embodiments, making use of various combinations of computers embedded within the concentrators and the RFID readers themselves. Further, the above description relates to a variety of hardware and software functions and components to accomplish those functions. In many cases, components that are described as hardware in a preferred embodiment may be replaced by software capable of performing the function of the hardware, and vice versa. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely by reference to the claims that follow. 

1. A networked radio frequency identification system for localizing an RFID tag at an endpoint represented as E.sub.i comprising: a plurality of radio frequency identification (RFID) tag readers, each RFID tag reader including at least one adjustable setting selected from RF signal strength, antenna gain, antenna polarization, and antenna orientation, and each RFID tag reader including a radio frequency (RF) interrogator; a computer in signal communication with the plurality of RFID tag readers over a network; and a software module for storage on and operable by the computer that localizes RFID tags based on information received from the RFID tag readers using hierarchical threshold limit calculations; wherein the hierarchical threshold limit calculations are based on accumulated reading factors from groups of settings for the RFID tag readers, wherein the software module is configured to: collect data for each setting of the RFID tag readers during an interval of time; calculate an aggregate result for each RFID tag reader based on an algorithm that uses a weighting function that includes W.sub.k,l and NR.sub.k,l as parameters where NR.sub.k,l represents the number of RFID tag readings at an interrogator ‘k’ configured with a setting ‘l’ and W.sub.k,l represents a weighting factor assigned to the interrogator ‘k’ configured with the setting ‘l’, and the algorithm spans all settings ‘l’ for the interrogator ‘k’; aggregate the calculated aggregate results based on a second weighting function to determine an aggregation result for an endpoint; and compare the aggregation result for the endpoint to at least one of a threshold value or threshold interval to determine whether the RFID tag is localized at the endpoint.
 2. The system of claim 1, wherein groups of the RFID tag readers are configurable to have a group setting and wherein the hierarchical threshold limit calculations are based on accumulated reading factors from settings of groups of RFID tag readers.
 3. The system of claim 2, wherein the software module is configured to: collect data for each group setting of a group of RFID tag readers during an interval of time; calculate an aggregate result for each group setting based on an algorithm that uses a weighting function that includes W.sub.k,l and NR.sub.k,l as parameters where NR.sub.k,l represents the number of RFID tag readings at an interrogator ‘k’ configured with a group setting ‘l’ and W.sub.k,l represents a weighting factor assigned to the interrogator ‘k’ configured with the group setting ‘l’, and the algorithm spans all group settings ‘l’ for the interrogator ‘k’; aggregate the calculated aggregate results based on a second weighting function to determine an aggregation result for an endpoint; and compare the aggregation result for the endpoint to at least one of a threshold value or threshold interval to determine whether the RFID tag is localized at the endpoint.
 4. A networked radio frequency identification system for localizing an RFID tag at an endpoint represented as E.sub.i comprising: a plurality of radio frequency identification (RFID) tag readers, each RFID tag reader including at least one adjustable setting selected from RF signal strength, antenna gain, antenna polarization, and antenna orientation, and each RFID tag reader including a radio frequency (RF) interrogator; a computer in signal communication with the plurality of RFID tag readers over a network; and a software module for storage on and operable by the computer that localizes RFID tags based on information received from the RFID tag readers using probabilistic threshold calculations; wherein the probabilistic threshold calculations are based on accumulated probabilities from groups of settings for RFID tag readers, wherein the software module is configured to: collect data for each setting of the RFID tag readers during an interval of time; calculate an aggregate result for each RFID tag reader based on an algorithm that uses a weighting function that includes W.sub.k,l and P.sub.k,l as parameters where P.sub.k,l=PF.sub.k,l(NR.sub.k,l, C.sub.k,l) is the probability that the RFID tag is at endpoint E.sub.i as detected from interrogator ‘k’ with settings ‘l’ calculated with the function PF.sub.k,l with NR.sub.k,l representing the number of RFID tag readings at interrogator ‘k’ configured with settings ‘l’ and C.sub.k,l representing a reference reading value for interrogator ‘k’ configured with settings ‘l’ and where W.sub.k,l represents a weighting factor assigned to the interrogator ‘k’ configured with the settings ‘l’, and the algorithm spans all settings ‘l’ for the interrogator ‘k’; aggregate the calculated aggregate results based on a second weighting function to determine an aggregation result for an endpoint; and compare the aggregation result for the endpoint to at least one of a threshold value or threshold interval to determine whether the RFID tag is localized at the endpoint.
 5. The system of claim 4, wherein groups of the RFID tag readers are configurable to have a group setting and wherein the probabilistic threshold calculations are based on accumulated probabilities from settings of groups of RFID tag readers.
 6. The system of claim 5, wherein the software module is configured to: collect data for each group setting of a group of RFID tag readers during an interval of time; calculate an aggregate result for each group setting based on an algorithm that uses a weighting function that includes Wk,l and Pk,l as parameters where P.sub.k,l=PF.sub.k,l(NR.sub.k,l, C.sub.k,l) is the probability that the RFID tag is at endpoint E.sub.i as detected from interrogator ‘k’ with group settings ‘l’ calculated with the function PF.sub.k,l with NR.sub.k,l representing the number of RFID tag readings at interrogator ‘k’ configured with group settings ‘l’ and C.sub.k,l representing a reference reading value for interrogator ‘k’ configured with group settings ‘I’ and where W.sub.k,l represents a weighting factor assigned to the interrogator ‘k’ configured with the group settings ‘l’, and the algorithm spans all group settings ‘l’ for the interrogator ‘k’; aggregate the calculated aggregate results based on a second weighting function to determine an aggregation result for an endpoint; and compare the aggregation result for the endpoint to at least one of a threshold value or threshold interval to determine whether the RFID tag is localized at the endpoint.
 7. A method of localizing an RFID tag using a system that includes a plurality of radio frequency identification (RFID) tag readers each of which includes at least one adjustable configuration setting selected from RF signal strength, antenna gain, antenna polarization, and antenna orientation, a computer in signal communication with the plurality of RFID tag readers over a network, and a software module for storage on and operable by the computer, the method comprising: collecting data for each setting of the RFID tag readers during an interval of time; calculating an aggregate result for each RFID tag reader based on an algorithm that uses a weighting function that includes W.sub.k,l and NR.sub.k,l as parameters where NR.sub.k,l represents the number of RFID tag readings at an interrogator ‘k’ configured with a setting ‘l’ and W.sub.k,l represents a weighting factor assigned to the interrogator ‘k’ configured with the setting ‘l’, and the algorithm spans all settings ‘l’ for the interrogator ‘k’; aggregating the calculated aggregate results based on a second weighting function to determine an aggregation result for an endpoint; and comparing the aggregation result for the endpoint to at least one of a threshold value or threshold interval to determine whether the RFID tag is localized at the endpoint.
 8. A method of localizing an RFID tag using a system that includes a plurality of radio frequency identification (RFID) tag readers which include at least one adjustable group configuration setting selected from RF signal strength, antenna gain, antenna polarization, and antenna orientation, a computer in signal communication with the plurality of RFID tag readers over a network, and a software module for storage on and operable by the computer, the method comprising: collecting data for each group setting of a group of RFID tag readers during an interval of time; calculating an aggregate result for each group setting based on an algorithm that uses a weighting function that includes W.sub.k,l and P.sub.k,l as parameters where P.sub.k,l=PF.sub.k,l(NR.sub.k,l, C.sub.k,l) is the probability that the RFID tag is at endpoint E.sub.i as detected from interrogator ‘k’ with group settings ‘l’ calculated with the function PF.sub.k,l with NR.sub.k,l representing the number of RFID tag readings at interrogator ‘k’ configured with group settings ‘l’ and C.sub.k,l representing a reference reading value for interrogator ‘k’ configured with group settings ‘l’ and where W.sub.k,l represents a weighting factor assigned to the interrogator ‘k’ configured with the group settings ‘l’, and the algorithm spans all group settings ‘l’ for the interrogator ‘k’; aggregating the calculated aggregate results based on a second weighting function to determine an aggregation result for an endpoint; and comparing the aggregation result for the endpoint to at least one of a threshold value or threshold interval to determine whether the RFID tag is localized at the endpoint.
 9. A method of localizing an RFID tag using a system that includes a plurality of radio frequency identification (RFID) tag readers which include at least one adjustable group configuration setting selected from RF signal strength, antenna gain, antenna polarization, and antenna orientation, a computer in signal communication with the plurality of RFID tag readers over a network, and a software module for storage on and operable by the computer, the method comprising: collecting data for each group setting of a group of RFID tag readers during an interval of time; calculating an aggregate result for each group setting based on an algorithm that uses a weighting function that includes W.sub.k,l and NR.sub.k,l as parameters where NR.sub.k,l represents the number of RFID tag readings at an interrogator ‘k’ configured with a group setting ‘l’ and W.sub.k,l represents a weighting factor assigned to the interrogator ‘k’ configured with the group setting ‘l’, and the algorithm spans all settings ‘l’ for the interrogator ‘k’; aggregating the calculated aggregate results based on a second weighting function to determine an aggregation result for an endpoint; and comparing the aggregation result for the endpoint to at least one of a threshold value or threshold interval to determine whether the RFID tag is localized at the endpoint.
 10. A method of localizing an RFID tag using a system that includes a plurality of radio frequency identification (RFID) tag readers each of which includes at least one adjustable configuration setting selected from RF signal strength, antenna gain, antenna polarization, and antenna orientation, a computer in signal communication with the plurality of RFID tag readers over a network, and a software module for storage on and operable by the computer, the method comprising: collecting data for each setting of the RFID tag readers during an interval of time; calculating an aggregate result for each RFID tag reader based on an algorithm that uses a weighting function that includes W.sub.k,l and P.sub.k,l as parameters where P.sub.k,l=PF.sub.k,l(NR.sub.k,l, C.sub.k,l) is the probability that the RFID tag is at endpoint E.sub.i as detected from interrogator ‘k’ with settings ‘l’ calculated with the function PF.sub.k,l with NR.sub.k,l representing the number of RFID tag readings at interrogator ‘k’ configured with settings ‘l’ and C.sub.k,l representing a reference reading value for interrogator ‘k’ configured with settings ‘l’ and where W.sub.k,l represents a weighting factor assigned to the interrogator ‘k’ configured with the settings ‘l’, and the algorithm spans all settings ‘l’ for the interrogator ‘k’; aggregating the calculated aggregate results based on a second weighting function to determine an aggregation result for an endpoint; and comparing the aggregation result for the endpoint to at least one of a threshold value or threshold interval to determine whether the RFID tag is localized at the endpoint. 